Isopropenyl-alpha,alpha-dimethylbenzyl isocyanate or TMI.RTM. Unsaturated Isocyanate, a product of American Cyanamid Company under the trade name TMI.RTM. (meta) Unsaturated Aliphatic Isocyanate, is a monomer which has two distinct reactive groups, a vinylic group and an isocyanate group. TMI.RTM. Unsaturated Isocyanate occurs as the meta isomer, para isomer or mixtures of meta and para isomers. The meta isomer of TMI.RTM. isocyanate is represented by the formula: ##STR1##
Grafting is an art recognized process in which a reactive material, usually a monomer or an oligomer, is attached onto a graftable material, usually a polymer having a reactive site or a functional group capable of reacting with the reactive material to be grafted. The reaction by which grafting takes place can be, without limitation, any reaction which allows two materials to combine. Most frequently, however, it is a free radical reaction.
Homografting is defined herein as a grafting process in which only a monomer of one type (viz. TMI.RTM. Unsaturated Isocyanate) is used as the reactive material, resulting in a homografted polymer having one or more groups pendently attached to the graftable polymer.
Cografting is defined herein as a grafting process in which more than one monomer is used as the reactive material resulting in a cografted polymer having groups derived from monomers as well as one or more comonomers, such as copolymeric groups pendantly attached to a graftable polymer.
Grafting of isopropenyl-alpha, alpha-dimethylbenzyl isocyanate onto isocyanate-reactive polymers via the isocyanate functionality has been mentioned in U.S. Pat. Nos. 4,766,185, 4,839,230, and 4,579,911 producing polymers having pendant isopropeny; groups. The cited patents however do not mention free radical homografting or cografting to produce polymers with pendant NCO groups.
The possibility of extrusion grafting of polyolefins with meta-isopropenyl alpha,alpha-dimethylbenzyl isocyanate via the isopropenyl group is disclosed in "Plastics Technology", November 1989, p. 13. Free radical grafting of meta-isopropenyl-alpha, alpha-dimethylbenzyl isocyanate onto polyolefins, polystyrene, acrylics, and polyesters has also been disclosed in "Modern Plastics", December 1989, page 16 with no mention of cografting.
Grafting saturated and unsaturated polymers with isopropenyl-alpha, alpha-dimethylbenzyl isocyanate or with isopropenyl-alpha, alpha-dimethylbenzyl isocyanate in combination with a cografting comonomer is disclosed in a copending application entitled "Isopropenyl-alpha, alpha-dimethylbenzyl Isocyanate-Grafted Polymers."
European Patent Application No. 185,606, published on Jun. 25, 1986, discloses a free-radical initiated grafting of a thioester synergist adduct of meta-isopropenyl-alpha, alpha-dimethylbenzyl isocyanate onto a styrene-butadiene rubber via the isopropenyl group. The grafted polymer product of the disclosure, however, is not isocyanate-functional. Furthermore, the grafting process is of low efficiency due to the poor reactivity of the isopropenyl group. Finally, the disclosure makes no reference to cografting with meta-isopropenyl-alpha,alpha-dimethylbenzyl isocyanate or adducts in combination with a cografting comonomer. Emulsion polymerization of meta-isopropenyl-alpha, alpha-dimethylbenzyl isocyanate is also disclosed in Eur. Pat. No. 194,222.
Copending United States Patent application No. 07/571,801 filed Aug. 23, 1990 describes the preparation of graft copolymers containing TMI.RTM. Unsaturated Isocyanate.
It is the object of this invention to provide a process for the preparation of isocyanate-functional latexes by homografting a graftable latex with isopropenyl-alpha, alpha- dimethylbenzyl isocyanate, or cografting in combination with a cografting comonomer at low temperatures.